1. Field of the Invention
The present invention relates to a method for manufacturing a discharge tube and a discharge lamp having the discharge tube.
2. Description of Related Art
A conventionally known discharge lamp, for example, a high-pressure mercury lamp, has a quartz discharge tube including a discharge part in which mercury and a rare gas are sealed, electrodes provided inside the discharge part and sealing parts formed at both ends of the discharge part.
In such a conventional high-pressure mercury lamp, in particular, the sealing parts of the discharge tube used therein can be formed by heating and softening portions to be the sealing parts of a straight quartz tube, which is a material for the discharge tube, and sealing them by pinching or shrinking.
A laser beam achieves a higher working accuracy than a commonly-used gas burner. Thus, it has been suggested that the laser beam be used as a heat source for heating and softening the quartz tube so that a high-quality discharge tube that is highly resistant to sealing pressure can be obtained (see JP 57(1982)-109234 A and JP 2997464 B).
However, such a conventional method for manufacturing the high-pressure mercury lamp using the laser beam has had the following problems. That is, especially when manufacturing a discharge tube with a long sealing part, since the laser beam can heat only a part of the quartz tube serving as a workpiece, it takes too long to heat and soften a long portion to be the sealing part of the quartz tube entirely, thus lowering a production efficiency. Also, since a high-power laser beam is needed to heat and soften the entire long portion to be the sealing part in a sufficient manner, the size of the device increases, resulting in higher cost.
It is an object of the present invention to solve the problems described above and to provide a low-cost method for manufacturing a discharge tube, by which a high-quality discharge tube that is highly resistant to pressure can be obtained and the production efficiency can be improved. It is a further object of the present invention to provide a discharge lamp including a low-cost discharge tube that is highly resistant to pressure.
A method for manufacturing a discharge tube of the present invention, the discharge tube including a discharge part, a sealing part formed at an end of the discharge part and an electrode provided in the discharge part, includes inserting an electrode body having the electrode into a portion to be the sealing part, which is adjacent to a portion to be the discharge part, of a transparent insulating tube serving as a material for the discharge tube, and sealing the portion to be the sealing part by heating and softening with a combination of a laser beam and a gas burner, thus forming the sealing part.
This makes it possible to select suitably the laser beam and the gas burner serving as heat sources for heating and softening the portion to be the sealing part according to each region in the portion to be the sealing part. In particular, by using the laser beam for a portion requiring a high working accuracy in the portion to be the sealing part, for example, the end of the portion to be the sealing part on the side of the portion to be the discharge part, it is possible to achieve an airtight sealing without any distortion, thereby obtaining a high-quality discharge tube that is highly resistant to pressure. Also, by using the gas burner having a larger heat capacity and a wider heating range than the laser beam for portions other than the above-noted portion requiring a high working accuracy, it is possible to seal a wide range of region in a short time, thus improving a production efficiency. In addition, by limiting the region to be heated and softened with the laser beam to the portion requiring a particularly high working accuracy, it becomes possible to use a laser beam having a lower output power. This allows a miniaturization of the device and a cost reduction.
Furthermore, a discharge lamp of the present invention includes a discharge tube obtained by the above-mentioned manufacturing method of the present invention. This makes it possible to provide a low-cost discharge lamp including a discharge tube that is highly resistant to pressure.